The present invention relates to a method, an electronic control unit, a vehicle control system, and a working machine for controlling a working machine having a bucket as a work implement. The term ‘power source’, which is described in the following text, is exemplified by an internal combustion engines such as a diesel engine. This should be regarded as a non-limiting example of such a power source.
Such a working machine as a wheel loader or a skid-steer loader is provided with a bucket as a work implement and at least one ground-engaging element such as wheels. The engine in the working machine is used for powering both the movement of the bucket via a hydraulic system and the movement of the machine via a traction system of the machine. Consequently, the operator is constantly challenged to balance the power given to the hydraulic system and the traction system by controlling the hydraulic levers (ex. lift and tilt levers of a wheel loader) and the gas pedal of the working machine. This is a general challenge for the operator of a working machine in which the engine is used for powering both the hydraulic system and the traction system.
A working machine is often used in a repeated work cycle. The term ‘work cycle’ comprises a route of the working machine and a movement of a work implement. For a working machine with a bucket such as a wheel loader, a short loading cycle is highly representative of the majority of applications. The archetype of the short loading cycle is bucket loading of a granular material such as gravel on an adjacent dump truck within a time frame of 25 to 35 seconds, which varies depending on how the work place is set up and how aggressively the operator uses the machine.
Including the short loading cycle, almost every work cycle of a wheel loader comprises a bucket filling phase during which the bucket is filled with granular material such as gravel of the gravel pile or any other objects that the wheel loader works with.
In order to fill the bucket with granular material, the operator needs to control three motions simultaneously: a forward motion of the wheel loader to penetrate into the gravel pile (traction), an upward motion of the bucket (lift) and a rotating motion of the bucket to fit in with as much granular material as possible (tilt). This is similar to how a simple manual shovel is used. However, in contrast to a manual shovel, these three motions cannot be directly controlled by the operator of a wheel loader, in spite of being observed. Instead, the operator has to use different subsystems of the machine in order to accomplish the task. The gas pedal controls the traction system, while the lift and tilt levers control the hydraulic system to yield lifting and tilting motions of the bucket.
During a bucket filling phase, the general challenge of balancing the hydraulic system and the traction system by controlling the gas pedal and hydraulic levers becomes more complicated. This is because the power delivered to the traction system does not only decrease the remaining power usable for the hydraulic system, but also directly prevent the lifting motion of the bucket due to a strong interaction between the forces originating from the two systems.
Penetrating the gravel pile with the bucket requires the traction force exerted by the bucket, which is originating from the traction system. When the bucket is about to be filled with gravel from the gravel pile, the bucket is physically connected to the ground, since the gravel pile is stuck to the ground. Due to this fact, the traction force creates a reaction force acting on the bucket in accordance with Newton's Third Law of Motion, the Law of Reciprocal Actions, and the reaction force acts to cancel out the lifting force originating from the hydraulic system.
Due to the fact that the force from the hydraulic system is cancelled out by traction in such a manner during the bucket pilling phase, the traction force must be carefully applied and the operator should reduce the traction force when the bucket is stuck in the gravel pile. However, when having the bucket stuck in the gravel pile and the lifting effort goes in vain, the obvious reaction for the operator would be to push the gas pedal more deeply in order to get more engine speed and thus “make the machine stronger”. However, this will just make the situation worse: more traction force will be created, which counteracts the lifting effort even more and the working machine consumes fuel without any useful work. Actually, the operator must do the counter-intuitive thing and lighten up on the throttle in order to reduce the engine speed.
The fact that the lifting force is cancelled out by traction in such a manner and the operator must do the counter-intuitive thing during the bucket filling phase yields several problems.
The working machine will be experienced as a weak machine and a machine of poor operability by the operator, especially by an inexperienced one, who will have a negative impression accordingly.
As the operability is poor, the operator will not be able to operate the machine in a productive, yet fuel-efficient manner. This poor operability and lack of fuel efficiency are not the problems pertaining only to inexperienced operators. The bucket can sometimes be stuck in the gravel pile even when the machine is operated by an experienced operator. In that case, of course, the experienced operator will get out of the situation more quickly with proper operation compared to other inexperienced operators. However, the unnecessary fuel consumption due to the situation that the bucket is stuck in the gravel pile is unavoidable.
In this regard, FIG. 1 illustrates fuel consumption during a short loading cycle of a conventional wheel loader driven by an experienced operator. The test results show that the fuel consumption rate (FC rate) is approximately 60% higher during the bucket filling phase than the cycle average (mean FC rate). Expressed in absolute values, the bucket filling accounts for 35˜40% of the mean total fuel consumption per cycle, yet the time spent for filling the bucket is only 25% of the average cycle time. Through FIG. 1 showing the fuel consumption during the operation by an experienced operator, it is understandable that more fuel will be consumed during the bucket filling phase when the machine is operated by an inexperienced operator.
Accordingly, when considering the problems related to the bucket filling phase and the results from FIG. 1 showing that the fuel efficiency is relatively low during the bucket filling phase, no matter whether the operator is skillful or not, there is a need to enhance fuel and work efficiencies by looking closely at the bucket filling phase.
The present invention was designed according to the necessity of an in-depth analysis of the bucket filling phase for the improvement of fuel efficiency and operational convenience. It is desirable to make a working machine operated in a productive, yet fuel-efficient manner by increasing its efficiency for easy operation even by inexperienced operators and by preventing unnecessary fuel consumption during the bucket filling phase.
According to an aspect of the present invention, a method is provided for controlling a working machine provided with a bucket as a work implement by which a lifting force can be exerted on an object such as a gravel pile, and at least one ground engaging element by which a traction force can be exerted on the same object, wherein the lifting force is an upward-directed lifting force experienced by the object. The method comprises the steps of:
receiving a state input indicative of a current bucket state, a bucket height being a parameter of the current bucket state,
determining a lifting force eliminating speed of a power source (LFES) at the current bucket state, the LFES being the speed at and above which no lifting force could be achieved considering a reaction force acting on the bucket caused by the traction force, and
controlling the speed of the power source not to reach the LFES in order that at least some lifting force could be achieved.
An aspect of the present invention also relates to an electronic control unit (ECU) being adapted to perform any of the method steps according to the method. Furthermore, an aspect of the present invention relates to a vehicle control system comprising the ECU, and a working machine comprising the vehicle control system.
According to another aspect of the present invention, a method is provided for controlling a working machine provided with a bucket as a work implement by which a lifting force can be exerted on an object such as a gravel pile, and at least one ground engaging element driven by one or a plurality of electric or hydrostatic wheel motors by which a traction force can be exerted on the same object, wherein the lifting force is an upward-directed lifting force experienced by the object. The method comprises the steps of:
receiving a state input indicative of a current bucket state, a bucket height being a parameter of the current bucket state,
determining a lifting force eliminating torque of the wheel motor(s) (LFET) at the current bucket state, the LFET being the torque at and above which no lifting force could be achieved considering a reaction force acting on the bucket caused by the traction force, and
controlling the torque of the wheel motor(s) not to reach the LFET in order that at least some lifting force could be achieved.